Vaginas Host Dynamic Battleground for Microbes, Study Finds

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The human vagina is a lively place, full of beneficial bacteria
that discourage nasty microbes from invading. Now, new research
finds this ecosystem is even more mysterious than previously
realized.

Not only do women vary widely in what sorts of microbes call the
vagina home, the study finds, but the ecosystem
of the vagina can also change rapidly — to no ill effect.
That's important, because while some vaginal infections are
associated with changes in the vagina's native flora, it's now
clear that not every change is a sign of disease.

"I think people are going to be surprised at the extent of
variation that we see in these species, and that practitioners
and women alike are going to see why they don't behave like their
sisters or their daughters or the last patient that they saw,"
said study researcher Larry Forney of the University of Idaho.

The vaginal ecosystem

Researchers have increasingly come to realize that without the
help of the microbes that live on our skin, in our guts and even
in our reproductive systems, humans would be in trouble.
Disruptions in gut bacteria have been linked to everything from
obesity to
depression, for example.

One of the most famous residents of the vagina is a group of
bacteria called Lactobacillus, which produces lactic
acid and helps keep the pH of the vagina around 4.5 — about the
same acidity as the juice of a tomato. But studies have shown
that at least five different types of bacterial communities that
can colonize a woman's vagina. Types 1to 3 are dominated by
Lactobacillus species, while the last two types are a
diverse bunch without many Lactobacillus. White women
are more likely to host a type 1 colony, dominated by
Lactobacillus crispatus, than black women, who more
often harbor diverse type 4 colonies. [ 10
Odd Facts About the Female Body ]

Now, Forney, his colleague Jacques Ravel of the University of
Maryland and their collaborators have shown that this vaginal
microbial "fingerprint" changes over time in individual women,
with one colony type displacing another, sometimes quite rapidly.
The researchers analyzed vaginal microbe samples, taken by a swab
twice a week for 16 weeks from 32 women. The women also kept
daily diaries of their activities and hygiene.

"With 32 women, we can capture almost all the different types of
communities that we have observed in previous samples," Ravel
said.

The researchers analyzed the genes of the microbes discovered in
order to identify them. They found that the vaginal ecosystem
varies widely over time, sometimes changing
during menstruation, sometimes swapping from one colony type
for another as a result of sexual activity or unknown reasons. In
some women, monthly bleeding didn't perturb the microbes at all;
in others, the period heralded a short-lived era in which on
microbe would reign supreme, only to be replaced when the
bleeding ended by another species that dominated the rest of the
month.

"We know that different women have different kinds of vaginal
microbiota, and now we know that over time the dynamics of the
change that we observed vary," Ravel told LiveScience.

Unique vaginas

The unstable world of the vagina is more than a scientific
curiosity. Disruptions in the vaginal "microbiome" have been
linked with bacterial vaginosis, a common condition sometimes
marked by itching, unusual discharge and unpleasant odor.
[ The
Sex Quiz: Myths, Taboos and Bizarre Facts ]

The problem, said William Ledger, a gynecologist at Weill Cornell
Medical College, is that about half of women who get a diagnosis
of bacterial vaginosis have no symptoms at all — laboratory tests
mark them as having an out-of-whack vaginal ecosystem, and most
doctors respond with antibiotics to bring the vagina back to
"normal." But the new study shows that it's actually
fluctuations, not stability, that are normal for many women.

"What we're saying is there can be
changes in the flora," said Ledger, who was not involved in
the original study put penned an opinion piece published
alongside it. "We think that women are probably in most cases
able to modify these changes and get back to what their normal
status is and that they shouldn't be treated [if they don't have
symptoms]."

The research showed that even as microbes change, their essential
functions might not, Ravel said. If you assume that the only
healthy vagina is a Lactobacillus-colonized vagina, you
might assume that if you don't see Lactobacillus
present, the woman is ill. In fact, other species may take up the
acid-generating slack in the absence of Lactobacillus,
the researchers found.

"We hope that by using more personalized treatments based on what
a woman looks like over time, you can actually start preventing
disease instead of just curing [it]," Ravel said."It can have a
lot of implications in medicine, for example, reducing the use of
antibiotics."

Mystery remains about what drives the changes in a woman's
vaginal ecosystem. Unlike gut or skin bacteria, vaginal bacteria
don't get outside sources of nutrients such as food or lotions
(with the possible exception of vaginal lubricants), Forney said.
Initial colonization probably happens at birth, but the bacterial
colonies change during puberty and menopause, he said. Estrogen
levels,
sexual activity and menstruation likely all play a role in
short-term fluctuations.

"It's a remarkable system in that it tends to stay within certain
boundaries," Forney said. "You don't see the system just come
apart. It comes back. It's a very resilient system."

That resilience and the specific bacteria that tend to show up
suggest an evolutionary selection for bacteria that help women
survive and pass on their genes in some way, Forney said. Besides
the microbes' role in preventing vaginal infections, they may
also play a role in fertility and childbirth, protecting the
infant during labor, for example, Ravel said, though that is "all
speculation." [ 5
Reasons Being a Woman Is Good for Your Health ]

The researchers are now studying a larger group of women and
collecting daily vaginal samples to better understand how fast
change happens. One hundred and sixty women are already enrolled
and have sampled their vaginas on a daily basis for 10 weeks,
Ravel said. The goal is both to understand any changes that come
before a vaginal infection, and to unravel the mysteries
of the microbiome more broadly, he said.

"One of our main drivers in some of the next-step questions that
we are taking on is trying to understand the true function of the
vaginal microbiota," Ravel said.